This invention relates to a lighting system, and, more particularly, to a system in which the light source has a suitable structure for generating a light which can be transformed by other components of the system so that a predetermined beam-pattern is provided.
Lighting systems generating pre-determined beam-patterns for the illumination of a target requiring a well-defined beam-pattern are widely used in practice for example as automotive headlamps, aircraft headlamps, locomotive headlamps, water craft headlamps or air traffic taxi lights. The light has a pre-determined beam-pattern when, for example and not exclusively, a cut off may be designed into the pattern of the beam. Most often, halogen incandescent lamps or recently high intensity discharge lamps with fused silica arc chambers are used in these lighting systems in order to meet the specific requirements set up for the light source component. U.S. Pat. No. 5,597,232 discloses a reflector lamp in which the light source is a metal halide lamp. The reflector lamp provides pre-determined beam-pattern and the arc chamber of the metal halide lamp, as it is known to an expert skilled in the art, is made of fused silica.
The metal halide lamp in lighting systems of this kind are highly overloaded in order to accomplish the required optical performance. Due to the overload, the useful life of the light source component is shorter. This life is also influenced by the severe ambient temperature conditions which originate from the required compactness of these lighting systems. The metal halide light sources suffer from short life at high operating temperatures owing to the devitrification of the arc chamber material and to the cracking of the seal area. This leads to giving up the useful life of the light source component for its performance which results in an inadequate life or in the need of relatively frequent replacement of the light source.
Ceramic metal halide lamps are a new generation of high performance, high intensity discharge light sources offering superior characteristics compared to the light sources mentioned above. The ceramic metal halide lamps have only been used for general lighting applications so far. In the past, designers might be prejudiced against the use of ceramic metal halide lamps in lighting systems for generating pre-determined beam-pattern owing probably to the relatively great size and diffuse light of these lamps. Although, a reflector lamp using a ceramic metal halide light source is described by U.S. Pat. 5,744,901. In the reflector lamp disclosed, the ceramic discharge vessel of the lamp is secured in the reflector body made of glass. This reflector lamp however is not capable of providing a pre-determined beam-pattern of light. Its pattern of beam cannot be designed to have for example a cut off which is a must e.g. for an automotive low beam headlamp.
It is therefore seen to be desirable to provide a lighting system for generating pre-determined beam-pattern which has a longer useful life and requires less maintenance cost.
In an exemplary embodiment of a first aspect of the present invention, a lighting system for generating pre-determined beam-pattern comprises a reflector body for reflecting the light forwardly thereof, an optical means for receiving and transmitting said reflected light, a discharge lamp and a lamp base. The discharge lamp is positioned between the reflector body and the optical means. The discharge lamp comprises a sealed discharge vessel made of ceramic light-transmitting material and contains an ionizable fill. The discharge lamp has at least one leg, a pair of spaced-apart electrodes within the discharge vessel between which an electric discharge is developed when the lamp is operated. The lamp base provides for supporting and positioning the discharge lamp, and includes contact elements for connecting the discharge lamp to an operating circuit.
In an exemplary embodiment of a second aspect of the present invention, the lighting system for generating pre-determined beam-pattern also comprises an operating circuit for igniting the discharge lamp and providing for steady state operation thereof. The sealed discharge vessel has means for making the discharge lamp at least approximately a point-like light source. The lamp base includes contact elements for connecting the operating circuit to a power supply.
This system has a number of advantages over the prior art represented by U.S. Pat. No. 5,597,232. One advantage is that the useful life of the system is extended. Another advantage is that it has an increased reliability and requires less maintenance cost. A further advantage is that the light projected by this system has a better color consistency, color stability and color separation properties. The efficiency and lumen maintenance of the system is also increased.
By properly matching the design and the dimensions of the ceramic metal halide light source and the components of the optical system responsible for the generation of the required pre-determined beam-pattern, a significant improvement is accomplished in the performance of such lighting systems. From light source side, several modifications are made on the current ceramic metal halide light source designs that make ceramic metal halide technology more suitable for its application to systems generating predetermined beam-pattern.